1. b Field of the Invention
The present invention relates to a fluid delivery system with particular application to an electroplating system.
2. Background of the Related Art
Semiconductor processing systems typically require fluid delivery apparatus to supply chemicals and other fluids to various components of the processing system. For example, electroplating involves the use of an electrolytic solution to plate a conductive surface formed on device features of a substrate. The substrate is positioned in a processing chamber, or cell, to expose a surface of the substrate to the electrolytic solution. The cell typically includes a cell body, an anode and a cathode on which the substrate is mounted. The solution is flowed into the cell and over the exposed surface of the substrate while a power supply biases the surface of the substrate with respect to the anode and solution to attract ions from the electrolytic solution, thereby plating the surface with a metal, such as copper. After flowing past the substrate, the fluid is emptied into a fluid source such as a tank or reservoir and then cycled back to the cell. In order to maintain a uniform chemical composition, the electrolytic solution is continuously circulated between the processing cells and the fluid source which also acts to replenish the chemical components of the electrolytic solution. Thus, a continuous supply of the electrolyte can be flowed past the substrate.
FIG. 1 is a simplified schematic of an electrolyte delivery system 10. A main tank 12 provides a bulk source of an electrolytic solution. The composition of the solution in the main tank 12 is controlled by a dosing module 14 which supplies the various constituents of the solution in the desired proportions. A supply line 16 couples the main tank 12 to processing cells 18 located downstream wherein substrates (not shown) are disposed during processing. A pump 17 disposed in the supply line 16 causes the solution to flow from the main tank 12 to the cells 18. The electrolytic solution is flowed through the cells 18 and subsequently expelled from the cells 18 via outlet lines 20. The outlet lines 20 dispense the electrolyte to an electrolyte return module (ERM) 22 which is fluidly coupled to the main tank 12 by a return line 24. A pump 26 disposed in the return line 24 pumps the spent electrolyte from the ERM 22 back to the main tank 12.
One problem with current fluid delivery systems, such as the system 10 shown in FIG. 1, is the use of pumps 17, 26 to circulate the fluid from the main tank 12 to the cells 18 and back to the main tank 12. Pumps 17, 26 are typically positive displacement pumps employing the use of diaphragms to provide lift at a suction inlet and pressure at an outlet. Such pumps require periodic maintenance or replacement as components, such as the diaphragm, become worn. Additionally, pump components, such as the diaphragm, are a source of contamination for the electrolyte as the components degrade over time. The resulting contamination can become lodged in device features formed on the substrate during processing and lead to defective devices. While filtration systems may be used to capture and remove larger particles from the electrolytic solution, some particles are too small for state-of-the-art filtration equipment. As the device geometry's continue to shrink the relative size of particles becomes larger.
Another problem with the use of pumps is the detrimental effect on the flow rate of the electrolyte over the surface of the substrate. In order to ensure uniform plating over a substrate surface at a constant rate, the flow rate of electrolytic solution in the cells must be maintained substantially constant during processing. However, the rapid action of pumps creates massive impulses in the system resulting in pulsed flow of the electrolyte in the cell. Thus, the flow pulses caused by the pumping action of the pumps causes the flow rate of solution in the cells to vacillate. Further, the pulsed flow can also force particles through filters disposed in the delivery system, thereby rendering the filters ineffective even for larger particles normally captured by the filters. Thus, the use of pumps in a fluid delivery system can present considerable cost in parts, labor, down-time and defective devices.
Therefore, there is a need for a fluid delivery system which eliminates or minimizes contamination of the fluid as well as flow pulses by use of components such as pumps.